A sexual fetish as follows:
The dominant male, after drinking some liquid prior, takes a pair of forceps (as used to help deliver babies) and uses them to forcibly hold open the submissive woman or man's anus to a width suitable for urinating into. He them urinates into the dilated asshole, filling it with urine. the forceps are then removed, and the anus allowed to close fully. The recipient of the asspiss is then allowed the great pleasure of passing the urine out his or her anus, as if defecating, only liquid. This process is quickly growing in popularity, and looks set to move mainstream within the next few years.

man: "hey bitch! I'm gonna give you an asspiss whether you like it or not!"
woman: "yes master, I crave your urine"